When the user operates a telescope for optical observation, typical examples of which may include monoculars and binoculars, in order to watch an object, holding the device with her/his hands especially in an airplane or in a train, vibrations from the airplane or the train are brought to bear on the case of the telescope, which causes hands movement of the user. The hands movement causes a change in the angle of a beam emitted by the observed object to the optical axis of the telescope. As a result, the quality of the image of the observed object, or the optical image, may deteriorate in such a manner that the image is blurred, or the resolution of the telescope becomes apparently lowered. Even if the magnitude of the vibrations transmitted to the telescope, such as monoculars and binoculars, is small, the optical image that makes an appeal to the eyes deteriorates in the end. It is because telescopes have a narrow field of vision, the image produced by the objective lens is magnified by the eyepiece, and the magnified image is subjected to observation. Thus, as the magnifying power of a telescope becomes large, changes in the angle of a beam emitted by an observed object to the optical axis of the telescope and deterioration in the quality of the observed image, caused by factors such as vibrations, become unignorable.
So far have been proposed various image stabilizers to compensate for deterioration in the quality of an observed image caused by changes in the angle of a beam emitted by the observed object to the optical axis of the telescope, which changes are caused by hands movement of the user.
Patent document 1 discloses an image-stabilizing optical device, a conventional telescope with image stabilization. The device has optical systems comprising a left-and-right pair of objective lenses, a left-and-right pair of eyepieces, and a left-and-right pair of erecting prisms respectively arranged between the left objective lens and the left eyepiece, and between the right objective lens and the right eyepiece; a prism holder for holding the left-and-right pair of erecting prisms; a gimbal suspension system for rotatably supporting the prism bolder so as to allow rotation of the prism holder about two orthogonal axes in a plane that is perpendicular to the optical axis and located between the objective lenses and the eyepieces; and a gyro motor fixed to the gimbal suspension system.
The image-stabilizing optical device disclosed in patent document 1 holds a left-and-right pair of erecting prisms with a single prism holder. The prism holder is mounted on the gimbal suspension system that is driven by a single gyro motor. This structure is capable of simplifying the driving mechanism of the image-stabilizing optical device.
On the other hand, this device has a serious problem: When this image-stabilizing optical device attends to, for example, lateral movements of the optical device, the prism holder is pivoted around the middle position between the erecting prism in the left optical system and the erecting prism in the right optical system, or the vertical axis running through the intersection O in FIGS. 1 and 4 of patent document 1. This pivoting causes the erecting prism in the left optical system to move, for example, toward the objective lens, whereas the erecting prism in the right optical system is moved toward the eyepiece. Then, the distance between the objective lens and the erecting prism in the left optical system becomes different from the distance between the objective lens and the erecting prism in the right optical system. As a result, how an observed object is seen through the right optical system is different from how the same object is seen through the left optical system. In other words, this image-stabilizing optical device disclosed in patent document 1 makes the arrangement of the optical components in the right optical system different from that of the optical components in the left optical system, when it deals with lateral movements. This difference results in a difference between how an observed object is seen through the right optical system and how the same object is seen through the left optical system.
The image stabilizer disclosed in patent document 2 has the same optical systems as the image-stabilizing optical device disclosed in patent document 1: The stabilizer has a left-and-right pair of objective lenses; a left-and-right pair of eyepieces; a left-and-right pair of erecting prisms respectively arranged between the left objective lens and the left eyepiece, and between the right objective lens and the right eyepiece; a prism holder for holding the left-and-right pair of erecting prisms; a gimbal suspension system for rotatably supporting the prism holder so as to allow rotation of the prism holder about two orthogonal axes in a plane that is perpendicular to the optical axis and located between the objective lenses and the eyepieces; and an angular velocity detector, placed in the prism holder, for detecting the angle of rotation of the gimbal suspension system, which is caused by vibrations applied to the telescope. The stabilizer rotates the gimbal suspension system so as to return the system to a predetermined position based on the detected angle in order to correct blurred images caused by the vibrations.
The image stabilizer disclosed in patent document 2 employs, as an actuator of the gimbal suspension system, a driving mechanism including a rotating motor for rotating the shafts of the gimbal suspension system, in place of the gyro motor. Thus the image stabilizer is supposed to achieve weight saving and downsizing, and to reduce power consumption. When the image stabilizer has the same lateral vibrations as the image-stabilizing optical device disclosed in patent document 1, however, the arrangement of the optical components in the right optical system is different from that of the optical components in the left optical system. This image stabilizer does not resolve the difference between how an observed object is seen through the right optical system and how the same object is seen through the left optical system.
Patent document 3 discloses an optical device for observation, which is actually a pair of binoculars, comprising a left-and-right pair of objective lenses; a left-and-right pair of eyepieces; a left-and-right pair of variable-angle prisms respectively arranged between the left objective lens and the left eyepiece, and between the right objective lens and the right eyepiece; a sensor for detecting vibrations of the mainframe of the device; actuators for respectively driving the left variable-angle prism and the right variable-angle prism; and a controlling circuit for determining the amount of the angle that each actuator changes in relation to the vertical angle of the prism, depending on the vibrations.
Patent document 4 discloses image-stabilized binoculars, comprising a left-and-right pair of objective lenses; a left-and-right pair of eyepieces; a left-and-right pair of correcting lenses respectively arranged between the left objective lens and the left eyepiece, and between the right objective lens and the right eyepiece; a sensor for detecting vibrations of the mainframe of foe device; an actuator for simultaneously driving the left and right correcting lenses; and a controlling circuit for determining the travel distances that the actuator drives the correcting lenses, depending on the vibrations.
Although the image stabilizing methods disclosed in patent documents 3 and 4 advantageously make the mechanisms smaller, the amount of a change in the angle of a beam emitted by the observed object to the optical axis of an optical device that can be corrected by the methods is small compared with that of the change that can be corrected by the methods disclosed in patent documents 1 and 2. The latter methods are applicable to a wider variation of situations.